The overall objective of this research is to elucidate the molecular mechanism on the self-assembly of the ribosome by studying the molecular recognitions and interactions of ribosomal proteins L25 and L18 with the 5S RNA molecule. Specifically we plan to investigate the following aspects of the ribosomal 5S RNA-protein complex: (1) The acquisition of the unique native conformation of the 5S RNA and those of ribosomal proteins L25, L18, and L5. Further studies on their native conformation, characterizations of the unfolded or "nascent" state, and their refolding to the native state under appropriate conditions will be studied. (2) The thermodynamics stability of the 5S RNA-protein complex by binding studies, and the conformation changes of the proteins and the 5S RNA upon protein-RNA interactions. (3) The molecular architecture of the 5S RNA-protein complex. We plan to decipher the contact regions of the 5S RNA and proteins by photochemical crosslinking and by tritium labelling. (4) Studies on the binding of 5S RNA fragments and the protein fragments of L25 and L18, which are the regions involved in RNA-protein interaction assembly. The results of the proposed research will enhance our general knowledge on the molecular mechanism of the recognition and interaction of protein and nucleic acids which is essential for the understanding of the structure-function of the many protein-nucleic acid systems involve in important cellular processes.